diff --git a/kallithea/lib/auth_modules/auth_internal.py b/kallithea/lib/auth_modules/auth_internal.py
--- a/kallithea/lib/auth_modules/auth_internal.py
+++ b/kallithea/lib/auth_modules/auth_internal.py
@@ -67,6 +67,9 @@ class KallitheaAuthPlugin(auth_modules.K
             log.warning("userobj:%s extern_type mismatch got:`%s` expected:`%s`",
                      userobj, userobj.extern_type, self.name)
             return None
+        if not username:
+            log.debug('Empty username - skipping...')
+            return None
 
         user_data = {
             "username": userobj.username,
diff --git a/kallithea/lib/auth_modules/auth_pam.py b/kallithea/lib/auth_modules/auth_pam.py
--- a/kallithea/lib/auth_modules/auth_pam.py
+++ b/kallithea/lib/auth_modules/auth_pam.py
@@ -85,6 +85,9 @@ class KallitheaAuthPlugin(auth_modules.K
         return True
 
     def auth(self, userobj, username, password, settings, **kwargs):
+        if not username:
+            log.debug('Empty username - skipping...')
+            return None
         if username not in _auth_cache:
             # Need lock here, as PAM authentication is not thread safe
             _pam_lock.acquire()